Linear beam microwave tube having means coupled to the beam upstream of input coupler and/or downstream of output coupler for varying amplitude and/or phase of r.f. component in the beam

ABSTRACT

A linear beam microwave tube comprises circuit element means coupled to the beam at a region between the electron gun and the input coupler and/or at a region between the output coupler and the collector. The circuit element means varies the amplitude and/or the phase of an r.f. component produced by an r.f. input power in the beam at the input coupler. The circuit element means may either be r.f. resistive means or resonator circuit means.

United States Patent 11 1 Tanalka et al.

1451 Aug. 26, 1975 221 Filed: June 14, 1974 211 App]. No.: 479,286

[30] Foreign Application Priority Data June 22, 1973 Japan 48-71128 June 22, 1973 Japan 48-71129 June 22, 1973 Japan 48-74599 June 22, 1973 Japan 48-74600 [52] US. Cl. SIS/5.39; 315/5.5l; 3l5/5.52 [51] Int. Cl. HOIJ 25/10 158] Field of Search 315/5.34, 5.35, 5.39, 5.43,

BIS/5.44, 5.46, 5.51, 5.52

[56] References Cited UNITED STATES PATENTS 2,916,659 12/1959 Sege 315/5.34 3,447,018 5/1969 Schmidt 3l5/5.52 X 3,502,934 3/1970 Friedlandcr et a1. 315/5.52 X 3,509,412 4/1970 Demmcl 315/5.52 X 3,509,413 4/1970 Schmidt 315/5.51 X- Primary Examiner-Saxfield Chatmon, Jr. Attorney, Agent, or Firm-Ostrolenk, Faber, Gerb & Soffen [57] ABSTRACT A linear beam microwave tube comprises circuit element means coupled to the beam at a region between the electron gun and the input coupler and/or at a region between the output coupler and the collector. The circuit element means varies the amplitude and/or the phase of an r.f. component produced by an r.f. input power in the beam at the input coupler. The circuit element means may either be r.f. resistive means or resonator circuit means.

11 Claims, 14 Drawing Figures Z a a LINEAR lBEAM MICROWAVE TUBE HAVING MEANS COUPLED TO THE BEAM UPSTREAM OF INPUT COUPLER AND/OR DOWNSTREAM OE OUTPUT COUPLER FOR VARYING AMPLITUDE AND/OR PHASE OE RJF. COMPONENT IN THE BEAM BACKGROUND OF THE INVENTION This invention relates to a linear beam microwave tube, which may be a multicavity klystron widely used in various fields where high output power is required over a wide operating frequency band.

A microwave tube of the type described comprises an electron gun, an input coupler, an output coupler, and a collector arranged in alignment in the order described. The tube further comprises means directing an electron beam from the gun to the collector successively through input and output couplers. The input coupler couples r.f. input power to the beam to produce therein an r.f. component. The output coupler derives r,f. output power from the r.f. component produced in the beam. Each of the input and output couplers may comprise a resonator circuit having interaction gap means contributing to the interaction between the r.f. power and the beam. The electron beam forming means may comprise magnetic focussing means for providing a focussing magnetic field substantially between the electron gun and collector. In general, the tube still further comprises several drift tubes extending around the beam from the interaction gap means.

In a microwave tube of the type described, for example, in a multicavity klystron having at least one intermediate resonator circuit between the input and output couplers, it is already known that a weak backwardly flowing electron stream is present in addition to the forwardly flowing electron beam. In static operation (without application of the r.f. input power to the input coupler), the backwardly flowing electron stream is produced by secondary electrons produced, in turn, by electrons of the forwardly flowing beam impinging on the collector and drift tubes. With the r.f. input power supplied to the input coupler, the velocity modulation of the beam electrons results in a deep density modulation of the beam at the interaction gap of the output coupler so that the beam provides a high r.f. output power to the output coupler and that the average velocity of the beam electrons decreases accordingly. It follows therefore in r.f. operation that some of the beam electrons are directed backwards from the output coupler interaction gap due to the deep velocity modulation the beam electrons are subjected to and by the velocity-decreasing phase of the electric field produced across the output coupler interaction gap. In addition, some of the beam electrons are repelled backwards by the space charge force which has grown considerably large downstream of the output coupler interaction gap due to the reduced velocities of the beam electrons. The backwardly directed electrons are focussed by the beam forming means into the backwardly flowing electron stream, which interacts more or less with the resonator circuits.

The backward stream electrons are small in number as compared with the forward beam electrons and generally have an irregular velocity distribution. It follows therefore in general that the interaction of the backward electron stream with the resonator circuits, although irregular, is small and has only a minor effect upon the performance of the microwave tube. In some cases, the backward electron stream nevertheless feeds or couples an amount of energy back to the input coupler that cannot be neglected with respect to the r.f. input power. The backward coupling resulting from the backward electron stream may render the microwave tube performance unstable. The degree of instability depends, in a complex manner, upon the amount of the backward stream electrons, arrangement of the resona tor circuits, the Q-values thereof, the distribution of the focussing magnetic field, the level of the r.f. input power, and other operating conditions. Although scarce in sophisticated multicavity klystrons, the troubles resulting from the backwardly directed electron stream are serious in a collector potential depressed microwave tube, in a high-gain five or six-cavity klystron, or in a high efficiency klystron of recent design.

As a countermeasure for the troubles, means is disposed in accordance with Japanese Patent Publication No. 37-6181 in a drift tube interposed between two cavity resonators of a microwave tube of the type de scribed for suppressing the propagation of electromagnetic waves. As another countermeasure, some of the drift tubes are outwardly flared into the associated cav' ity resonators according to US. Pat. No. 3,447,018. These countermeasures may be effective in suppressing the feedback caused by the backwardly directed electrons on the input side of the microwave tube. It would, however, be inevitable with these countermeasures where the feedback suppressing means is disposed be tween the input and output couplers that the forward gain is also reduced in an amount related to the reduction in the feedback.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a microwave tube of the type described in which the backward coupling is substantially eliminated without serious adverse effect on the forward operating characteristics of the tube.

It is another object of this invention to provide a microwave tube of the type described, stably operable with a high forward gain and at a high efficiency.

In accordance with the present invention, a micro wave tube of the type described comprises circuit ele ment means coupled to the electron beam at a region between the electron gun and the input coupler and/or at a region between the output coupler and the collector for varying the amplitude and/or the phase of the r.f. component resulting in the electron beam primarily from the r.f. input power. The circuit element means automatically substantially eliminates the adverse effects otherwise caused on the tube performance by backwardly directed electrons.

It will be seen that the r.f. component amplitude and- /or phase varying means is disposed upstream of the input coupler and/or downstream of the output coupler rather than in a region therebetween where the r.f. am plification is carried out. The circuit element means may be disposed outside of a vacuum envelope of the tube, without any modification to the structure of the tube.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic axial sectional view of a conventional three-cavity klystron;

FIGS. 2A-2D show similar views of a conventional five-cavity klystron;

FIGS. 3A & 3B schematically show frequency characteristics of the klystron shown in FIGS. 2A-2D;

FIG. 4 is a schematic axial sectional view of a multicavity klystron according to a first embodiment of the instant invention;

FIG. 5 is a like view of a multicavity klystron according to a second embodiment of this invention;

FIG. 6 is a similar view of a multicavity klystron according to a modification of the second embodiment;

FIG. 7 is an enlarged schematic partial axially sectionalized view of a linear beam microwave tube according to a third embodiment of this invention;

FIG. 8 is a similar view of a linear beam microwave tube according to a modification of the third embodiment;

FIG. 9 is a similar view of a linear beam microwave tube according to a fourth embodiment of this invention; and

FIG. 10 is a similar view of a linear beam microwave tube according to a modification of the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Beforedescribing several preferred embodiments of the present invention, a linear beam microwave tube of the prior art will be briefly reviewed with reference to FIG. 1. Also, further description will be given with reference to FIGS. 1 and 2 of the backwardly directed electrons or the backwardly flowing electron stream mentioned in the preamble of the instant specification.

Referring more particularly to FIG. 1, an electron beam 10 is formed in a multicavity klystron by an electron gun 11 comprising a cathode 12 (having a heater element 12a), an anode 13 and a magnetic focussing device 16 comprising first and second pole pieces 17 and 18 and a plurality of coils, such as 19. The beam 10 flows in a forward direction along the klystron from the electron gun 11 to a collector 21 successively through a central opening formed through the first pole piece 17, a cavity resonator 22 of an input coupler, an intermediate cavity resonator 23, a cavity resonator 24 of an output coupler, and a central opening formed through the second pole piece 18. The cavity resonators 22, 23, and 24 have interaction gaps 27, 28, and 29, respectively. Within the focussing magnetic field produced by the magnetic focussing device 16, the ra' dius r,, of the beam 10 is approximately constant and is from 0.6 to 0.8 times the radius r of drift tubes, such as 31, extending either from or between the interaction gaps 27, 28, and 29. The input coupler comprises a loop 32 for supplying r.f. input power to the klystron to produce in the input coupler resonator 22 an r.f. electromagnetic field which, in turn, interacts with the beam 10 at the input coupler interaction gap 27 to produce r.f. velocity modulation 0n the beam 10. While drifting, the beam 10 is subjected to density modulation, which is enhanced by the interaction of the beam 10 with the intermediate resonator 23. The output coupler comprises a loop 34 for deriving r.f. output power from the output coupler resonator 24 in which the r.f. component of the deep density modulated beam produces an r.f. electromagnetic field at the output coupler interaction gap 29. The average velocity of the beam 10 accordingly decreases although the electrons of the beam 10 have their respective velocities determined by the phase of the r.f. component of the beam 10 at the output coupler interaction gap 29 and by their respective trajectories in the beam 10.

In a microwave tube of the type illustrated with reference to FIG. 1, the beam radius r,, does not appreciably grow large downstream of the output coupler interaction gap 29 when the klystron operates at low levels of the input signals. However, in large-signal operation, the interaction of the beam 10 with the output coupler resonator 24 becomes strong to increase the beam radius. As a result, some of the beam electrons tend to impinge on the interior surface of the drift tube extending forwardly from the output coupler interaction gap 29 to the collector 21. Even when these electrons do not actually impinge on the interior surface, some of the beam electrons will impinge on the upstream end interior surface of the collector 21. In this manner, the beam electrons behave in a complicated manner after their passage through the output coupler interaction gap 29 where they lose a substantial amount of energy and from that point foward they are subjected to a weaker focussing magnetic field. Summarizing, some of the beam electrons will be directed backwards as exemplified at 36 and secondary electrons will flow backwards as exemplified at 37. These backwardly directed or flowing electrons are subjected to the focussing magnetic field and proceed towards the electron gun 11 as an electron stream having a larger radius substantially extending across the entire radius of the drift tubes. In addition, the stream electrons which have various velocities and vary in amount from time to time, interact at the output coupler interaction gap 29 with the elec tromagnetic field induced by the beam 10 in the output coupler resonator 24, and further interact with the intermediate resonator 23, and feed the microwave energy back to the input coupler resonator 22. The feedback characteristics are complicated and unstable.

Even with the static operation of the klystron, some of the beam electrons return from the downstream end portion of the collector wall as exemplified at 38 although these rearward moving electrons seldom diverge wider than the beam radius r,,. This fact has now been confirmed by the fact that backward amplification of from to dB from the output coupler loop 34 to the input coupler loop 32 exists, which is appreciably smaller than the amplification presumable from the amount of the rearward moving electrons measured by the electron current flowing in the anode 13. The fact that the amplification is small means that the rearward moving electron flow has only small interaction with the resonator circuits and consequently has a small radius. In contrast, the feedback in large-signal operation often amounts to l0 dB of the r.f. input signal.

Referring to FIG. 2A, another conventional multicavity klystron comprises parts designated with similar reference numerals as in FIG. 1 and, instead of a single intermediate resonator 23, is provided with three intermediate resonators 231, 232, and 233 having interaction gaps 281, 282, and 283, respectively. Either when the r.f. output voltage is of the same order as the beam accelerating anode voltage or when the velocity of the velocity modulated electrons is distributed over a wide range, it has now been confirmed that a portion of the beam electrons does not reach the collector 21 but is directed backwards shown in FIG. 28, that some of the remaining beam electrons impinge on the inside surface of the drift tube extending forwardly of the' output coupler interaction gap 29 towards the collector 21 to produce a large number of secondary electrons which at least partly flow back towards the electron gun 11 as depicted in FIG. 2C, that even the still remaining beam electrons reaching the collector 21 produce secondary electrons which at least partly flow backwards as shown in FIG. 2D. It is to be noted here that the beam electrons still have an appreciable amount of the r.f. components even after their passage through the output coupler interaction gap 29 and that even the secondary electrons produced in the manner illustrated with reference to FIGS. 2C and 2D accordingly have r.f. components. The electron stream proceeding towards the electron gun 11 is subjected to modulation at the output coupler interaction gap 29 and then at the intermediate resonator interaction gaps 283, 282, and 281 to form feedback loops at the lattermentioned interaction gaps 281 through 283. In addition, the backward moving electron stream reaching the electron gun 11 is accelerated by the anode voltage to become an additional electron beam shown at 39 in FIG. 1 flowing towards the collector 21 and forming additional feedback loops. Although the backwardly proceeding electron stream is weak even when the r.f. output voltage is considerably high, it has been found that this electron stream .and additional electron beam have an undesireable effect upon the r.f. component of the beam at the output coupler interaction 'gap 29 to seriously adversely affect the klystron operation and to make the operation unstable.

Referring to FIGS. 2A2D and 3A3B, the facts have now been found which clearly evidence the presence of the complicated r.f. components at the output coupler interaction gap'29. More particularly, the klystron illustrated with reference to FIG 2A was operated as a four cavity klystron with the most upstream resonator 22 detuned to the operating passband of frequencies and supplied with no r.f. power and with the'second upstream resonator 231 supplied with the r.f. input power through aloop (not shown). The r.f. output power exhibited the characteristics shown in FIG. 3A. With the most upstream resonator 22 tuned to a frequency within the operating passband, a spike 40 amounting to +1 dB above the amplified level appeared in the characteristics as illustrated in FIG. 3B. The spike 40 moved with a shift in the frequency of fundamental mode of resonance of the most upstream resonator 22. This behavior of the spike 40' proves the presence of the r.f. component in the backward electron stream even outside of a region between the second upstream resonator interaction gap 281 and the output coupler interaction gap 29.

Referring now to FIG. 4, a multicavity klystron according to a first embodiment of the present invention comprises parts designated with like reference numerals as in FIGS. 1 and 2A. According to the first embodiment, the l lystronfurther comprises an input side r.f. attenuator 41 between the electron gun 11 and the input coupler resonator 22 and/or an output side r.f. attenuator 42 between the output coupler resonator 24 and the collector 21. The r.f. attenuator 41 or 42 may be provided either by making a portion or the whole of the relevant drift tube of a material havinglarge electric resistance or by forming a film of resistive material on the interior surface of the drift tube concerned. The

material for the r.f. attenuator tube 4] or 42 may be iron. stainless steel, a nickel-copper alloy known as Monel Metal, or the like. The r.f. attenuator film may be made by plating the interior surface of the relevant drift tube with the material mentioned above. Alternatively, the film may be made by spraying up the interior surface either powered stainless steel or a mixture of iron group metal powder and aluminum powder known by the name of Kanthal, a Swedish company.

In operation, the circuit element means provided by the output side r.f. attenuator 42 varies the amplitude of the r.f. component of the principal electron beam to reduce the r.f. component of that portion of the backward electron stream which is provided by the secondary electrons produced at the collector 21 or produced at locations adjacent thereto. In addition, the attenuator 42 directly reduces the r.f. component of the lastmentioned portion of the backward electron stream. The input side attenuator 41 reduces the r.f. components of both the entire backward electron stream and the additional forward electron beam, thereby varying the amplitude of the r.f. component of the electron beam 10 including the additional forward electron beam.

Referring to FIG. 5, a multicavity klystron according to a second embodiment of this invention is characterized by an r.f. circuit element 46 coupled to the electron beam 10 in a region between the electron gun I] and the input coupler resonator 22. In the example being illustrated, the r.f. circuit element 46 comprises an input side resonator circuit exemplified by a cavity resonator and disposed between the gun 11 and the input coupler resonator 22. The input side cavity resonator 46 is coupled to the electron beam 10 at its interaction gap 47 and is provided with a loop 48 connected to an adjustable load 49. The cavity resonator 46 may be either of substantially the same dimensions as the input coupler or intermediate resonators 22 and 23 or of smaller dimensions having the fundamental or harmonic mode of resonance within the operating passband of frequencies. Alternatively, the r.f. circuit ele ment may be coupled to the beam 10 either through a wave guide or a coaxial cable. The load 49 may be another resonator circuit, a stub tuner, a slug tuner, a pair of strip lines, or the like.

In operation, it should be reminded that the voltage appearing across the input coupler interaction gap 27 results from a superposition of a voltage resulting from the r.f. input power ofa first unwanted voltage resulting from the r.f. component of the backward electron stream with a second unwanted voltage resulting from the r.f. component of the additional forward electron beam. By adjusting the impedance of the load 49, it is possible to vary the amplitude and/or the phase of the r.f. component of the additional forward electron beam at a region between the input side resonator interaction gap 47 and the input coupler interaction gap 27. This, in turn, varies the amplitude and/or the phase of the r.f. component of the backward electron stream. In combination, the circuit element means provided by the r.f. circuit element renders it possible to vary the amplitude and/or the phase of the r.f. component of the backward electron stream and to reduce the first and second unwanted voltages. In other words, the circuit element means substantially eliminates the backward coupling and eliminates the instability of the microwave tube operation.

Referring to FIG. 6, a multicavity klystron according to a modification of the second embodiment comprises an output side cavity resonator 51 disposed between the output tnupler resonator 24 and the collector 21. The resonator 51 is coupled to the electron beam at its interaction gap 52 and is accompanied by a loop 53 connected to an adjustable load 54. As a further modification of the second embodiment, a multicavity klystron may comprise the output side r.f. circuit element 51 in addition to the input side r.f. circuit element 46 illustrated with reference to FIG. 5. In any event, the operation of the output side r.f. circuit element 51 is similar to that described in conjunction with the input side r.f. circuit element 46.

Referring to FIG. 7, a linear beam microwave tube according to a third embodiment of this invention comprises that interaction gap 47 of the input side cavity resonator 46 described in conjunction with the second embodiment (FIG. 5), which is formed between the anode 13 of the electron gun l1 and the free end of an input side drift tube 61 extending backwardly from the input coupler interaction gap 27 to the gun 11. In the example being illustrated, the anode 13 serves as a reentrant portion of the input side cavity resonator 46. The so-called top wall of the reentrant cavity resonator 46 is provided by a metal support 62 for the input sidev drift tube 61 sealed to a ceramic tube 65 forming a portion of a vacuum envelope of the microwave tube. The so-called bottom wall of the reentrant cavity resonator 46 is partially provided by another metal support 66 for the anode l3 sealed also to the ceramic tube 65. A peripheral wall 67 is extended between the top and bottom walls 62 and 66 to provide the remaining portion of the bottom wall and the so-called side wall of the reentrant cavity resonator 46. The dimensions of the cavity resonator 46 may readily be determined by experiment and/or calculation. Although operation of the third embodiment is similar to that described in connection with the second embodiment, it is worthwhile to note that the third embodiment is effective in keeping the distance between the input coupler and the electron gun and consequently the lengths of the microwave tube and of the magnetic focussing device 16 (see FIG. 1) small.

Referring to FIG. 8, a linear beam microwave tube according to a modification of the third embodiment comprises a ring 69 of an electrically insulating material disposed between the anode support 66 and the peripheral wall 67 described with reference to FIG. 7. This provides a choke coupling in the bottom wall of the reentrant cavity resonator 46. The choke coupling may be disposed between the drift tube support 62 and the peripheral wall 67 or elsewhere in the wall. of the resonator of any shape. The choke coupling enables the anode current to be measured to give an estimation of the backward electron stream.

Referring to FIG. 9, a linear beam microwave tube comprises an output side drift tube 71 extending downstream of the output coupler interaction gap 29 and a hollow collector 21 having an upstream end wall 72 defining an opening for the collector 21 opposing the free end opening of the output side drift tube 71. According to a fourth embodiment of this invention, the interaction gap 52 of the output side resonator circuit 51 is formed by that space between the opposing openings of the output side of drift tube 71 and of the upstream end wall 72 which is usually merely used to measure the beam transmission factor of the microwave tube. In the example being shown, the downstream end portion of the collector 21 serves as a reentrantof the cavity resonator 51. The downstream end of the reentrant cavity resonator interaction gap 52 is provided by the upstream end wall 72 of the collector 21, which is sealed to an output end ceramic tube 75 forming a portion of the vacuum envelope described in conjunction with the third embodiment. The top wall of ,the reentrant cavity resonator 51 is provided by a portion of a metal support 76 for the output side drift tube 71, which is also sealed to the output end ceramic tube 75. A peripheral wall 77 extends between the collector upstream end wall 72 and the drift tube support 76 to provide both the bottom and side walls of the reentrant cavity resonator 51. The dimensions of the resonator circuit 51 may be readily determined by experiment and/or calculation.

With reference to FIG. 6, it may be mentioned that a collector 21 must be made larger and thus inevitably heavier if spaced further apart from the output coupler interaction gap 29 because the electron beam 10 diverges here. With the fourth embodiment illustrated with reference to FIG. 9, it is possible to provide the output side resonator circuit 51 without lengthening the distance between the output coupler interaction gap 29 and the upstream end of the collector 21 and consequently without adversely affecting the strength of the hermetic seal for the collector 21.

Referring finally to FIG. 10, a linear beam microwave tube according to a modification of the fourth embodiment comprises a ring 79 of an electrically insulating material between the output side resonator circuit peripheral wall 77 and the collector side wall. This provides a choke coupling for electrically insulating the collector 21 from the output coupler resonator 24 to enable the measurement of the beam transmission factor of the microwave tube. The choke coupling may be disposed elsewhere in the output side resonator wall.

. While several embodiments of this invention and their modifications have thus far been described, it will readily be understood that other embodiments and modifications are possible within the scope of this invention. For example, the multicavity klystrons described with reference to FIGS. 4 through 10 may be other linear beam microwave tubes, such as travelling wave tubes. The circuit element means placed on one of the input and the output sides may be a plurality of r.f. attenuators and/or r.f. circuit elements. A microwave tube according to this invention may comprise the input and output side resonator circuits described with reference to FIGS. 7 through 10.

What is claimed is:

1. A microwave tube including an electron gun, an input coupler, an output coupler, a collector, and means for directing an electron beam flow from said gun toward said collector successively through said input and output couplers, said input coupler being adapted to couple r.f. input power to said beam to eventually produce an r.f. component in said beam at said output coupler, said output coupler being adapted to derive r.f. output power from said r.f. component, wherein theimprovement comprises circuit element means coupled to said beam in at least one of regions between said gun and said input coupler and between said output coupler and said collector for varying at least one of the amplitude and the phase of said r.f. component.

2. A microwave tube as claimed in claim 1, wherein said circuit element means comprises r.f. attenuator means.

3. A microwave tube as claimed in claim 2, wherein said r.f. attenuator means comprises a tube of an electrical resistive material surrounding said electron beam.

4. A microwave tube as claimed in claim 2, further comprising a drift tube extending from at least one of said input and output couplers towards said electron gun and said collector, respectively, wherein said r.f. attenuator means comprises a film of an electrical resistive material on the interior surface of said drift tube.

5. A microwave tube including an electron gun, an input coupler, an output coupler, a collector, and means for directing an electron beam flow from said gun toward said collector successively through said input and output couplers, said input coupler being adapted to couple r.f. input power to said beam to eventually produce an r.f. component in said beam at said output coupler, said output coupler being adapted to derive r.f. output power from said r.f. component, wherein the improvement comprises circuit element means coupled to said beam in at least one of regions between said gun and said input coupler and between said output coupler and said collector for varying at least one of the amplitude and the phase of said r.f. component; wherein said circuit element means is an r.f. circuit means comprising a cavity resonator, an adjustable load coupled to said cavity resonator, said cavity resonator having an interaction gap coupled to said electron beam.

6. A microwave tube as claimed in claim 5, further comprising a drift tube surrounding said electron beam and extending from said input coupler toward said electron gun, wherein said cavity resonator interaction gap is provided by a gap formed between the free end of said tube and said electron gun.

7. A microwave tube as claimed in claim 6, further comprising a pair of metal supports for said drift tube and an anode of said electron gun, wherein a pair of opposing walls and said cavity resonator are at least partly provided by said metal supports.

8. A microwave tube as claimed in claim 6, wherein said cavity resonator comprises a choke coupling in its wall.

9. A microwave tube as claimed in claim 5, further comprising a drift tube surrounding said electron beam and extending from said output coupler with its free end disposed adjacent to said collector, said collector being of a hollow type, wherein said cavity resonator interaction gap is provided by a gap formed between said drift tube free end and said collector.

10. A microwave tube as claimed in claim 9, further comprising a metal support for said drift tube, wherein one of the opposing walls of said cavity resonator is provided by said metal support.

11. A microwave as claimed in claim 9, wherein said cavity resonator comprises a choke coupling in its wall. 

1. A microwave tube including an electron gun, an input coupler, an output coupler, a collector, and means for directing an electron beam flow from said gun toward said collector successively through said input and output couplers, said input coupler being adapted to couple r.f. input power to said beam to eventually produce an r.f. component in said beam at said output coupler, said output coupler being adapted to derive r.f. output power from said r.f. component, wherein the improvement comprises circuit element means coupled to said beam in at least one of regions between said gun and said input coupler and between said output coupler and said collector for varying at least one of the amplitude and the phase of said r.f. component.
 2. A microwave tube as claimed in claim 1, wherein said circuit element means comprises r.f. attenuator means.
 3. A microwave tube as claimed in claim 2, wherein said r.f. attenuator means comprises a tube of an electrical resistive material surrounding said electron beam.
 4. A microwave tube as claimed in claim 2, further comprising a drift tube extending from at least one of said input and output couplers towards said electron gun and said collector, respectively, wherein said r.f. attenuator means comprises a film of an electrical resistive material on the interior surface of said drift tube.
 5. A microwave tube including an electron gun, an input coupler, an output coupler, a collector, and means for directing an electron beam flow from said gun toward said collector successively through said input and output couplers, said input coupler being adapted to couple r.f. input power to said beam to eventually produce an r.f. component in said beam at said output coupler, said output coupler being adapted to derive r.f. output power from said r.f. component, wherein the improvement comprises circuit element means coupled to said beam in at least one of regions between said gun and said input coupler and between said output coupler and said collector for varying at least one of the amplitude and the phase of said r.f. component; wherein said circuit element means is an r.f. circuit means comprising a cavity resonator, an adjustable load coupled to said cavity resonator, said cavity resonator having an interaction gap coupled to said electron beam.
 6. A microwave tube as claimed in claim 5, further comprising a drift tube surrounding said electron beam and extending from said input coupler toward said electron gun, wherein said cavity resonator interaction gap is provided by a gap formed between the free end of said tube and said electron gun.
 7. A microwave tube as claimed in claim 6, further comprising a pair of metal supports for said drift tube and an anode of said electron gun, wherein a pair of opposing walls and said cavity resonator are at least partly provided by said metal supports.
 8. A microwave tube as claimed in claim 6, wherein said cavity resonator comprises a choke coupling in its wall.
 9. A microwave tube as claimed in claim 5, further comprising a drift tube surrounding said electron beam and extending from said output coupler with its free end disposed adjacent to said collector, said collector being of a hollow type, wherein said cavity resonator interaction gap is provided by a gap formed between said drift tube free end and said collector.
 10. A microwave tube as claimed in claim 9, further comprising a metal support for said drift tube, wherein one of the opposing walls of said cavity resonator is provided by said metal support.
 11. A microwave as claimed in claim 9, wherein said cavity resonator comprises a choke coupling in its wall. 